The present invention relates to laser welding stainless steel components, in particular, laser welding high carbon martensitic stainless steel components and austenitic stainless steel components together by a stabilized ferritic stainless steel fusion zone modifier in the weld portion.
In a common laser welding process, metallic members are assembled with bonding surfaces in juxtaposition, for example, to form a butt joint, and one outer surface is scanned with a continuous laser beam to melt and fuse the members at the bonding surfaces. In contrast to other welding processes such as electrical resistance welding that generate heat concentrated at the bonding surfaces, laser welding heats a zone extending from the irradiated surface down below the touching surfaces to create a pool of molten metal within both members that, upon solidification, forms the weld nugget that joins the two metallic members together.
When high carbon martensitic stainless steel and austenitic stainless steel are laser welded together, the molten material in the fusion zone will be primarily an austenitic phase initially. Unless approximately a minimum of 3-5% delta ferrite is present during the solidification process, the potential for encountering micro-fissures or solidification cracks is high in the solidified fusion zone. As the cause of micro-fissures or solidification cracks is related to the absence of delta ferrite, it is necessary to balance the chemical compositions of the fusion zone to promote the presence of delta ferrite. Elements contained in each respective alloy to be welded can be balanced to produce a fusion zone devoid of micro-fissures or solidification cracks.
In order to obtain a weld portion having soundness and reliability between different types of metallic materials laser welded together, such as laser welding a high carbon martensitic stainless steel and an austenitic stainless steel together, the composition and structure of the weld material at the joint portion must be controlled. When a high density energy welding method having a small heat input quantity such as laser welding is used, the welding width and the depth of penetration is small. Because the melt quantity is small, it is expected that the absolute formation quantity of the fusion zone will contain sufficient content of delta ferrite when sufficient mixing and proper chemical balance is achieved. Accordingly, it is expected that laser welding different types of metallic materials together by obtaining a weld portion having sufficient soundness and reliability can be achieved by controlling the solidified structure formed in the weld portion. Attempts have been made in the prior art to attain an improved weld when laser welding different types of metallic materials together.
One attempt at laser welding different types of metallic materials together is disclosed in U.S. Pat. No. 5,628,449 issued to Onuma et al., wherein a method of laser welding carbon steel and austenitic stainless steel together by an austenitic stainless steel welding material is disclosed. The metallographic structure of the weld portion comprises a mixed structure of an austenitic structure and not greater than 20% of a ferritic structure. The composition of the weld material in Onuma et al. consists of, in terms of weight percentage, not greater than 0.15% of C, not greater than 0.65% of Si, 1.0 to 3.0% of Mn, 10-16% of Ni, 26-32% of Cr, and 1.0 to 5.0% of Mo as an optional component, the balance of Fe, and not greater than 0.02% of P and 0.02% of S as unavoidable impurities. However, Onuma et al. fail to teach laser welding high carbon containing martensitic stainless steel to austenitic stainless steel via a fusion zone modifier consisting of stabilized ferritic stainless steel material in the weld joint, thereby preventing or inhibiting the formation of solidification cracks and micro-fissures in the fusion zone, while maintaining mechanical properties of the weld joint, and some degree of immunity from environmental degradation.
There is a need to develop an improved laser welded fusion zone and laser welding process between two different metallic materials, such as a high carbon martensitic stainless steel, typically containing greater than about 0.8% carbon (expressed in terms of weight percentage), and an austenitic stainless steel, that is less susceptible to the formation of solidification cracks in the fusion zone, while maintaining mechanical properties, and some degree of immunity from environmental degradation. The inventor has developed a laser welding process that incorporates a stabilized ferritic stainless steel fusion zone modifier in a weld portion joining high carbon martensitic stainless steel and austenitic stainless steel via laser welding, capable of solving the aforementioned problems.
The present invention is directed to a laser welding process for joining high carbon martensitic stainless steel and austenitic stainless steel components by a stabilized ferritic stainless steel fusion zone modifier in the weld portion. The present invention is also directed to a method for preventing or inhibiting solidification cracks from forming in the weld joint portion of metallic materials that exhibit a high potential to form solidification cracks, such as when high-carbon martensitic stainless steel components and austenitic stainless steel components are laser welded together with out employing a stabilized ferritic fusion zone modifier in the weld joint portion.
Another object of this invention to provide a laser welded article comprising a high carbon martensitic stainless steel component and an austenitic stainless steel component laser welded together by a stabilized ferritic stainless steel fusion zone modifier in the weld joint portion in order prevent and/or inhibit solidification cracks from forming in the fusion zone laser weld, and assist immunity to environmental degradation.
It is a further object of this invention to provide improved elements and arrangements thereof for the purposes described which are inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.